This invention relates to providing zinciferous metal surfaces, i.e., surfaces of a metallic material that is at least 55% by weight zinc, with a corrosion protective coating by contacting the zinciferous surfaces with an aqueous acidic treatment composition containing fluorometallate anions and transition metal cations.
The general type of treatment compositions used in this invention was disclosed in Patent Cooperation Treaty International Publication WO/85/05131. Little attention was paid in that publication to maintenance of the treatment composition during extended use. It is now known, however, that zinc ions dissolve from the metal surface being treated and accumulate in used aqueous acidic treatment compositions of this type, thereby altering their composition. U.S. Pat. No. 5,344,504 of Sep. 6, 1994 to Deck et al. teaches that certain treatment compositions of this type operate satisfactorily even with zinc ions concentrations up to 30 grams per liter (hereinafter usually abbreviated as "g/L") and recommends operating processes using such compositions to treat zinciferous surfaces with little or no overflow, in order to minimize pollution problems. However, it has now been observed that such a method of operation leads to variations in the quality of the coatings produced and that such variations are unacceptable for some commercial operations.
A major object of the present invention is to provide an improved process for treating zinciferous surfaces with compositions containing transition metal cations and fluorometallate anions so as to minimize variations in the quality of the protective coatings formed thereby. Other objects will be apparent from the description below.
Except in the claims and the specific examples, or where otherwise expressly indicated, all numerical quantities in this description indicating amounts of material or conditions of reaction and/or use are to be understood as modified by the word "about" in describing the broadest scope of the invention. Practice within the numerical limits stated is generally preferred, however. Also, unless expressly stated to the contrary: percent, "parts of", and ratio values are by weight; the term "polymer" includes "oligomer", "copolymer", "terpolymer", and the like; the first definition or description of the meaning of a word, phrase, acronym, abbreviation or the like applies to all subsequent uses of the same word, phrase, acronym, abbreviation or the like and applies, mutatis mutandis, to normal grammatical variations thereof; the description of a group or class of materials as suitable or preferred for a given purpose in connection with the invention implies that mixtures of any two or more of the members of the group or class are equally suitable or preferred; chemical descriptions of neutral materials apply to the materials at the time of addition to any combination specified in the description and/or of generation in situ in a combination by chemical reactions described in the specification, and do not necessarily preclude chemical changes to the materials as a result of unstated reaction in the combination; specification of materials in ionic form means that the materials are supplied to prepare the compositions containing them in the form of soluble substance(s) containing the ions specified and implies the presence in any composition specified to contain ionic materials of sufficient counteroins to produce electrical neutrality for the composition as a whole; any counterions thus implicitly specified preferably are selected from among other constituents explicitly specified in ionic form, to the extent possible; otherwise such counterions may be freely selected, except for avoiding counterions that act adversely to an object of the invention.